The sight of a relatively bright star suddenly vanishing as a faint asteroid crosses in front of it, and then just as suddenly reappearing several seconds later is an exceedingly rare and startling celestial occurrence. But it's happening in the predawn hours on Tuesday and lucky skywatchers across parts of Canada and the western United States may have a chance to see it. Astronomers refer to such an event as an "occultation" — a temporary hiding of one celestial object by another such as a planet moving in front of a star as seen from Earth. In this particular case, however, the occulting body will be a minor planet: a tiny asteroid known as 824 Anastasia.
The star in question is Zeta Ophiuchi, the third brightest star in the constellation of Ophiuchus, the Serpent Holder. At magnitude +2.6, it's a star that's bright enough to easily see with the naked eye; you don't even need binoculars, although they would give a better view.